Circuit arrangement for the control of glow tubes



Feb. 14, 1939.

W. HAHNLE CIROUIT'ARRANGEMENT FOR THE CONTROL OF GLOW TUBES OriginalFiled May 28, 1930 IIIIIIIIIIIJVI Gill? 5* Patented Feb. 14, 1939 UNITEDSTATES PATENT OFFICE CIRCUIT ARBANGEDIENT FOR THE CONTROL OF GLOW TUBEStion of Germany Application May 28, 1930, Serial No. 456,314. Be-

newed December 18, 1936. In Germany June 1,

11 Claims. (Cl. 176124) In arrangements for the electric control of thebrightness of glow tubes, for instance in so-called writing tubes forthe purposes of picture telegraphy, the unsteadiness of the currentpotential characteristic of the glow tubes makes itself felt indisturbing manner in that the changes in intensity of the glow light donot faithfully follow 31:1 changes in the amplitude of the signal poten-According to the present invention, this fault is overcome bycompensating the resistance of the glow tube through the use ofamplifier tubes by means of feed-back, and insuring the stability of thecircuit arrangement by means of suitable negative feed-back energy.

Due to the feed-back or back-coupling the plate A. C. of the amplifiertube feeding the glow tube is rendered independent of the resistance ofthe glow tube loading circuit so that the glow tube current follows thecontrol potential linearly. The decrease in the stability of the circuitarrangement, caused by the bMk-coupling, is eliminated by negativefeed-back or a counter-coupling. It will thus be appreciated that thepotential returned to act on the grid of the amplifier will be equal tothe difference between the feedback voltage and the negative feedbackvoltage. Any change in the resistance characteristics of he glow lampwill cause a change in the difference of. the two potentials fed back tothe grid and by suitably porportioning these two energies, thecompensating voltage returned to the grid will be just equal to thatnecessary to counteract the change in the glow lamp resistance. Theinvention is illustrated in the circuit diagrams, Figs. 1 and 2 showingtwo embodiments by way of example.

In Fig. '1 a receiving tube l which receives energy from the inputcircuit 1, and a power tube 2 are coupled by resistance 3. In the platecircuit of power tube 2 are connected a winding part 4, used asauto-transformer, of a transformer and a small resistance 5 to which isconnected in parallel a transformer 6. The transformer 6 is providedwith the high-ohmic loading resistance The transformer circuit containstwo rectifiers 8, 8' which jointly feed the glow lamp 9 with rectifiedcurrent. From transformer winding 4 branches off a line Ill on whoseregulatable resistance ll may be taken oil the back-coupling. potentialand impressed on'the grid of tube I. In the circuit of the back-couplingline is also disposed the counter-coupling arrangement in the shape oftransformer 6 which likewise impresses on the grid of the first tube apartial amount of the plate circuit potential, of opposite phase to thatreturned by the connection to the potentiometer ll, of the power tube.

If in the course of the operation of the arrangement the characteristicof the glow tube moves 5 due to heating, that is, if its strikingpotential and its resistance value varies, the control potential isautomatically changed by the back-coupling and the counter-coupling insuch manner that the current is not influenced. This results from 10 thefact that the direct feed-back potential is proportional to the voltageappearing. at the output of the tube 2, while the negative feed-backpotential is proportional to the current flowing through the glow lamp9. The difference between these 15 two potentials which determines theamount of compensation, is accordingly, influenced by the resistance ofthe tube. For example, if the resistance of the tube increases, assumingthat the output voltage of the tube 2 is held constant, then 20 thepotential of the negative feed-back is less than it was formerly, sinceless current will flow through the lamp. Accordingly, therefore, thedirect feed-backpotential predominates, causing an increased voltage toappear at the output of 25 the tube 2, which, in effect, overcomes theincrease in resistance of the tube 9. If the resistance of the tube 9decreases, then more current will flow through the lamp and accordingly,a greater negative feed-back potential is provided 30 which reduces theactual potential actuating the grid of tube I, and accordingly, theoutput of the tube 2 is reduced to compensate for the decrease inresistance.

Fig. 2 shows a similar circuit arrangement, ex- 35 cept that in thiscase howeveronly the alternating potential is fed to the rectifiercircuit by means of a choke coil l2 and a condenser l3. In thisarrangement the operation is enhanced by compensating the potential dropproduced in the 40' pling transformer I4, whose primary winding isconnected in parallel with the ohmic resistance and whose secondary isdisposed in the backcoupling line.

Having now described my invention, what I claim and desire to secure byLetters Patent is the following 1. The method of controlling impedanceloads varying with changes in amplitude of the current passedtherethrough from an audion ainplifier which comprises supplying energyto the load from the audion output and feeding back to the audion inputa voltage determinable by the changes in impedance of the load due tovariations in amplitude of the output current, whereby the outputcurrent from the audion is determined from the signal potential inputand is independent of the load impedance.

2. In a system for supplying current to variable impedance devices, aplurality of resistance coupled amplifiers and an input circuittherefor, a

variable impedance element in the output of the second of saidamplifiers, and means associated with the output circuit of the secondamplifier for feeding back to the amplifier input circuit a voltagedeveloped in proportion to the changes in impedance of the load due tovariations in amplitude of the output current whereby the eflectiveoutput from said amplifiers is determined solely in accordance with theapplied signal potentials.

3. The method ofcontrolling glow tubes from,

an audion amplifier which comprises supplying therethrough, the step inthe method of maintaining the output current independent of valueof theload impedance which comprises feeding back to the input of the tube avoltage of suflicient magnitude and suitable phase to neutralize theefiect of changes with amplitude in the load impedance upon the normalplate current flow.

5. A method'of compensating for changes in impedance of a load circuitenergized from an audion amplifier, which comprises supplying energy tothe load circuit from the audion amplifier output, feeding back to theinput of the audion amplifier a portion of the output voltage thereirom,simultaneously feeding back to the audion input a counter-phase voltagevariable with changes in'impedance of the load due to variations inamplitudeof the output currentirom the audion amplifier, and controllingthe gain of the audion amplifier in accordance with the difference ofthe two out-of-phase energies fed back to the input of the audionamplifier.

q. A system for controlling the gain 4 in an amplifier for variations inimpedance of the load therein due to changes in the amplitude of thecurrent passing through the amplifier which comprises a thermionicamplifier, having aninput and an output circuit, means connecting avariable impedance to the output circuit of said amplifier, means forderiving a proportionate voltage from the output of said amplifier,means for deriving a voltagein accordance with the current flowingthrough said variable impedance, means for adding both of said derivedvoltages out of phase with each other, and means to impress thedifference between said derived voltages upon the input of saidamplifier.

7. In combination, a light producing device whose impedance is afunction of the amplitude of current passing therethrough, an amplifierfeeding the light producing device, and feedback means connected betweenthe light producing device and the amplifier to maintain the amplitudeof the current independent of the impedance of the light producingdevice.

8. In combination, a current responsive light producing device whoseimpedance is a function of the amplitude of the current passingtherethrough, a source of energy for energizing the light device andfeedback means for controlling the source of energy connected betweenthe light device and source of energy to maintain the amplitude ofthe'current independent of the impedance of the light producing device.

9. In combination, a linear amplifier, a nonlinear current-impedanceoperated light producing device, feedback means connecting the amplifierto the light producing device, and means for altering the linearity oithe amplifier to compensate for the non-linearity of the light device.

10. In combination, a linear amplifier having input and output circuits,a non-linear currentimpedance operated light producing device connectedin the output circuit, and means from the amplifier output circuit tothe input circuit for feeding back energy to the input circuit foraltering the linearity of the amplifier to compensate for thenon-linearity of the light device.

11. In combination, an alternating current amplifier having a pluralityof thermionic tubes, 9. variable light emitting device, a rectifier fedby energy from the amplifier and feeding energy to the variable lightemitting device, a voltage feedback circuit connected between therectifier and one of the thermionic tubes of the amplifier to controlthe energy fed by the amplifier to the rectifier in accordance with theenergy fed from the rectifier to the variable light emitting device.

WAL'I'ER

